> fn foo(n i32, m i32) (i32, i32) {}

But now consider returning a function with type¹

  Foo<T<string, T2>> -> (bool -> IDictionary<string, T3> -> i32 -> T3) where T2 : T3

even if you leave out the latter type constraint, I think it is hard to avoid undecidable ambiguity.

  fn foo(n i32, m T2) (????) {}

You quickly get ambiguity due to type parameters / generics, functions as arguments, and tuples if you don't syntactically separate them.

Even if you your context-depended parser can recognize it, does the user? I agree that a language designer should minimize the amount of muscle damage, but he shouldn't forget that readability is perhaps even more critical.

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1. Note, even if the parser can recognize this, for humans the '>' is confusing unless syntax highlighting takes care of it. One time it delimits a generic type argument, the other time it is part of '->'. This is also an argument for rendering these things as ligatures.